ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Dec. 1975, p. 751-753 Copyright 0 1975 American Society for Microbiology

Vol. 8, No. 6

Printed in U.S.A.

NOTES In Vitro Evaluation of a New Oral Cephalosporin, Cefatrizine (BL-S640) G. A. STILWELL, H. G. ADAMS, AND M. TURCK* Department of Medicine, University of Washington and Harborview Medical Center, Seattle, Washington 98104

Received for publication 28 August 1975

The activity of cefatrizine (BL-S640), a semisynthetic orally absorbed cephalosporin, was studied and found to have in vitro activity at least comparable to that previously reported for cephalexin.

The present studies were performed to assess the in vitro antibacterial activity of cefatrizine (BL-S640), a new semisynthetic orally absorbed cephalosporin (2, 6). Antibacterial activity was determined by antibiotic dilution methods performed in nutrient (Difco) and Mueller-Hinton (Difco) agar and broth. Studies in agar were performed by use of a Steers replicator device (4). The methods for performing the agar and broth dilution tests were described previously by this laboratory (3, 5). A total of 173 isolates of Enterobacteriaceae and 30 strains each of Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus were studied. The cumulative percentage of 53 isolates of Enterobacter and 30 isolates each of Klebsiella, Escherichia coli, Enterococcus, S. aureus, indole-positive Proteus, and Proteus mirabilis susceptible to increasing concentrations of cefatrizine is shown in Fig. 1 and 2, which also summarize the effects of medium and inoculum size on the antibacterial activity of this compound in agar. The results of these studies performed in agar demonstrate that cefatrizine at a concentration of 5.0 jig or less of antibiotic/ml inhibited all isolates of Klebsiella, E. coli, P. mirabilis, and S. aureus at both inoculum sizes of bacterial cells. In addition, activity was comparable in either agar medium. However, even when the smaller inoculum of organisms was employed, only 75% ofEnterobacter isolates were inhibited by 25 ug of cefatrizine/ml. Moreover, when tested against the smaller inoculum in nutrient agar, 75% of indole-positive Proteus isolates were inhibited by 24 ,ug of cefatrizine/ ml, whereas 100 ,ug of antibiotic/ml was required to inhibit a comparable number of these strains in Mueller-Hinton agar. Similarly, cefa751

trizine was more active against isolates of Enterococcus in nutrient agar medium. Although not shown, cefatrizine exerted negligible activity against P. aeruginosa, and all isolates grew in concentrations of 250 ,ug of cefatrizine/ml regardless of the medium or inoculum size of bacterial cells. Figures 3 to 6 summarize the minimal inhibitory concentration and minimal bactericidal concentration activity of cefatrizine against these same isolates tested in broth medium with two inoculum sizes of bacterial cells. Against all genera, cefatrizine appeared less active in broth than in agar. This difference was most 100-

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FIG. 1. Cumulative percentage of 53 isolates of Enterobacter and 30 isolates each of Klebsiella and E. coli inhibited by increasing concentrations of cefatrizine tested in agar medium with bacterial inocula of two different sizes.

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In vitro evaluation of a new oral cephalosporin, cefatrizine (BL-s640).

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Dec. 1975, p. 751-753 Copyright 0 1975 American Society for Microbiology Vol. 8, No. 6 Printed in U.S.A. NOT...
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